In numerous chemical processes catalysts are used which loose activity during the process and therefore lower yields are obtained. Generally, these catalysts have to be regenerated. As a result, the reactor or the reactors containing the catalyst has/have to be taken out of operation. Therefore, several publications are concerned with improvement of these processes.
WO 01/72729 and U.S. Pat. No. 6,727,371 B2 disclose a continuous process for reacting an organic compound with hydroperoxide in the presence of a catalyst, wherein the reaction is carried out in a reactor assembly comprising at least two reactors connected in parallel. One of the reactors can be taken out of operation to allow for regeneration of the catalyst whereas the other reactor is still operated to allow for a continuous process.
DE 10 2004 003 003.0 relates to a process for the continuous preparation of a chemical compound, in which a specially designed shell-and-tube reactor is used in at least one reactor used for the preparation of this compound. The use of two or more reactors connected in parallel is also disclosed.
WO 02/085873 discloses a process for the catalytic epoxidation of olefins with hydrogen peroxide in a continuous flow reaction system, wherein the reaction mixture is passed through a fixed catalyst bed in down-flow operation mode and the reaction heat is at least partially removed during the course of the reaction. The use of two or more reactors connected in parallel is also disclosed.
WO 02/085874 relates to a process for the catalytic epoxidation of olefins with hydrogen peroxide in a multiphase reaction mixture which can be conducted in several reactors connected in series or in parallel.
EP 1 403 259 A1 relates to a continuous process for the epoxidation of olefins using a heterogeneous catalyst for promoting the epoxidation reaction, whereby deactivation of the catalyst has been considerably reduced. The use of two or more reactors connected in parallel is also disclosed.
U.S. Pat. No. 5,760,253 and U.S. Pat. No. 5,840,933 relate to a reactor and a process for the production of oxirane compounds by reaction of an olefin such as propylene with an organic hydroperoxide using a solid contact catalyst, wherein the reactor is divided into a series of separate zones, each zone containing a bed of solid epoxidation catalyst. The use of reactors connected in parallel is not disclosed.
According to U.S. Pat. No. 5,912,367, propylene is converted to propylene oxide in a highly efficient liquid phase process wherein temperature and pressure are both increased over the course of the epoxidation, which is preferably conducted in a continuous mode of operation. The catalyst used is a heterogeneous catalyst such as titanium silicalite or titania-on-silica. The oxidizing agent is an active oxygen species such as hydrogen peroxide or an organic hydroperoxide. When the desired yield of propylene oxide can no longer be maintained, the catalyst is replaced or regenerated.
U.S. Pat. No. 5,849,937 discloses an olefin epoxidation process using a plurality of reactor vessels, each containing a fixed bed of a heterogeneous catalyst such as titania-on-silica. The reactor vessels are connected in series whereby a feedstream comprised of olefin and an active oxygen species is passed through said series of reactor vessels in contact with the heterogeneous catalyst to accomplish conversion of the olefin to the corresponding epoxide. As the activity of the catalyst in an individual reactor vessel falls to an undesirably low level, said reactor vessel is taken out of service and a replacement reactor vessel containing fresh or regenerated catalyst introduced. The replacement reactor vessel may, in alternative embodiments of the process, be the first or the last reactor vessel in said series. For example, the feedstream may first be contacted with either the most active or the least active charge of catalyst within the series of reactor vessels. The use of reactors connected in parallel is not disclosed.
Since the deactivation of the catalyst is believed to be a continuous process, the processes as disclosed in the state of the art still have losses in yield of the desired reaction product over the reaction time.
It is an objective of the present invention to provide a novel process for the preparation of an olefin oxide which is advantageous with respect to the overall yield in reaction product compared with state-of-the-art processes.